Method for recording sound



June 12,1923.

H. W. "NEBB METHOD FOR RECORDING SOUND Filed June 19, 1919 DIRECTION OF 7% OF PLATE I E1;g5.

INVENTOR ATTORNEY DIRECTION OF TRAVEL OF SHUTTER ll atented June 12, 1923.

EPA?

-. RTWELL W. WEBB, OF CRESSKILL, NEW JERSEY.

.METHOD FOR RECORDING SOUND. 7

Application filed .Tune 19, 1919. Serial No. 305,432.

To all whom it may concern Be it known that I, HARTWELL W. WEBB,

a citizen of the United States, residing at .Cresskill, in the county of Bergen and State of New Jersey, have invented certain new and useful Improvements in Methods for Recording Sound, of which the following is a specification.

This invention relates generally to sound recording and particularly relates to a new and improved method for producing sound phra-gm that is adapted to be vibrated by sound waves representing the sounds desired to be reproduced. From the sound record thus obtained, a master cameo record is made from which a multiplicity of sound records in a permanent form are produced by well-known processes. Although records made by the general methods referred to have gone into Wide and extensive use, it is in spite of the fact that, with a mechanical cutting tool it is impossible to faithfully represent the recorded sounds or tones with any close approach to theiroriginal purity or richness, not only because the weight and resulting inertia and momentum ofthe cutting member, through its physical and mechanical connection with the diaphragm, acts t damp the free vibration of the diaphragm in response to the action of the sound waves directed throughout, but also because of the resistance offered by the wax or equivalent material to the movement of the cutting tool therein. 7

It has long been recognized that, if an imponderable element, such as a ray of light,- could be substituted for the cutting tool, the serious objections attending the use of the cutting tool would be eliminated, and a very considerable step forward in the art of sound reproduction would have been achieved, provided, of course, that proper advantage had been taken of the situation and a suitable relief record evolved for use in subsequent reproduction of the recorded sounds. Many attempts have accordingly been made to utilize photographic methods for producinga sound record in black and white and of forming from the photographic record byv photo-engraving processes a record in relief by means of 80 which the sounds originally recorded could be reproduced. However, so far as I am aware, none of such attempts has been successfully developed to a point where the method chosen has gone into practical and commercial use. The reason for this has been due to a complete failure on the part of the experimenters to appreciate the 11ecessity for employing a recording light of a character and in a manner suited to the requirements of the work, that is, in such a way that a sufficiently intense exposure could be made on the rapidly moving sensitive surface, to affect the surface to the required degree, and which would be free to act unhampered by diffraction effects so as to produce a path of exposure? having sharply defined lateral edges.

In the course of experiments conducted for the purposes of the invention, 1 have discovered that a sufiicient exposure for the purpose can be'obtained by the use of a very intense source of artificial light placed comparatively near the sensitive surface which is to receive the record. In ,order to obtain the sharp and well-defined lateral light-path margins that are essential for the purpose, it is necessary that the source of light to be relatively minute, so that, coupled with the near relation to the sensi tized surface in which it'is placed, a condition can be secured by which with the aid, of suitable stop means a powerful beam of parallel rays can be obtained which, by means of a suitable sound-wave controlled orifice, can be projected against the recordreceiving surface undispersed and undiverted by diffraction efiects.

I have found that the character and unvarying intensity of light emitted from a short section of tungsten filament is well adapted for the purpose in view and that, because of the small compass in which a source of light of this type. can be provided,

it can be favorablyutilized by mounting the 1 light source comparatively near the recordreceiving surface, and preferably directly on the sound box framework of the reproducing machine or on the recording arm itself. Preferably the section of filament used is somewhat elongated in comparison to its width, and the length of the section is parallel to the sensitive surface and sub and that I can in this way produce a photographic effect that will automatically produce an approximately V or semi-elliptical groove section which isbetter adapted for the purpose than would be a rectangular or approximately rectangular section.

From the photographic record made by the use of the apparatus referred to a negative is developed in which the recorded sounds are represented by an undulating opaque spiral line. From this record a posi tive is printed and developed in a wellknown manner and, by a preferred method,

I expose a film of gelatine sensitized with ammonium dichromate to light passing through the positive plate and develop the dichromated gelatine to produce a record in relief from which a master record, suitable for use in the production of commercial reproduein records, can be produced.

In the rawings,

Figure 1 is a side elevation'of a portion of a photographic recording apparatus embodying the form of a part of my invention;

Figure 2 is a plan view, partly broken away, of the device shown in Figured;

Figure 3 is an enlarged sectional View showing a preferred form of light-projecting means employed in the initial recording p;

Figure 4 shows on an enlarged scale a variety of forms of orifice that may be employed in the light-controlling shutter;

Figure 5 shows on an enlarged scale the relation that exists between the section of filament serving as a light source and the relative direction of movement of the shutter and the plate;

Figure 6 shows a side elevation of a modified form of mounting for the recording lamp; and I Figure 7 is an end view, partly'in section and partly in elevation, of the device shown in Fi re 6.-

I have illustrated in the drawings at 1 in Figure 1 the turntable of a recording machine on which may be placed a plate or film 2 having a light-sensitized upper surface. The turntable and the sensitized plate carried thereby are adapted to be rotated about a vertical axis so that a sound box 3 associated therewith, when given a movement along a radius drawn from the axis of rotation of the plate, will trace a spiral path in a manner well exemplified in talkin machine records of the disc type.

In order to produce in the sensitized surface of the plate a light tracing that will represent the movements of the diaphragm 4 of the sound box 3 in response to the sound waves acting thereon, a source of light-preferably taking the form of an electric incandescent lamp 5, is mounted in a tubular support 6 attached to a bracket 7 carried directly by the sound box 3, as shown in Figures 1 and 2. In order to control the action of light on the plate in accordance with the movements of the diaphragm, I employ a shutter, preferably taking the form of a disk 9 carried at the end of a lever 1O between the lower. end of the lamp 5 and the plate 2'. The lever 10 is preferably pivoted at 11 on the margin of the sound box 3 and connected intermediate its ends to the diaphragm, so that the vibrations of the diaphragm are transmitted 'to the shutter which is reciprocated in a path transverse to the length of the section of filament 8 to thereby produce in the lighttraced path lateral undulations correspond-- ing to the movements of the diaphragm.

I provide for securing an adequate intensity of light for the purpose by making use of a tungsten filament 8 because of the high actinic value and intense and'unvarying character of the light given off by an incandescent filament of this type, and also by mounting the lamp in such a position that the filament is placed at a distance of approximately one-half of an inch from the sensitized surface of the plate 2. I still further add to the effectiveness of the illumination furnished by the light by making use of the comparatively elongated section of filament 8 the width of which is approximately the same as or very little in excess of the groove inthe finished record or be tween .003 and .006 of an inch and whose active length is about double its width, which I place in a parallel position with relation to the plate 2 and with its length lying in the direction of movement of the plate. By means of suitable light-controlling means hereinafter referred to, I provide that the cross-section of the light beam reaching the plate has the general formation of the sector of filament comprising the light source, and by reason of the fact that the elongated lightspot lies with its length in the direction of travel of the plate, an overrunning or overlapping of the light spot along the path of the beam is secured, which has the effect of Reference has already been made to the importance of producing a light-traced path having sharp and clean-cut lateral edges, and it will be seen that by reason of the location of the source of light in the immediate vicinity of the sensitized surface, I am able to obtain a beam of rays that is diverted to a minimum degree by the effects of diffraction. In order to still further insure that a beam of parallel rays is provided, I preferably-make use of a lightdirecting aperture 12 of'relatively substantial length 1n comparison with its width and having a uniform cross-section from end to end. The use of this construction has the effect of passing the beam of light through two separated and spaced apart aligned openings of equal size and thus procuring a beam of rays that are substantially parallel,

stylus of the reproducing machine.

so that a short beam of uniform section is obtained between the exit end of the aperture and the surface of the plate in which the diaphragm-controlled orifice is placed in such close adjacency to the surface of the plate that the effects of diffraction on the light beam reaching the plate through the orifice are, for all practical purposes, completely nullified.

I preferably provide for producing a greater illumination in the center of the line than at the lateral margins in such progressively-increasing proportions as to determine the securing of a V-shaped or semielliptical groove section in the reproducing records finally obtained. I procure this desir'able result by means of the particular conformatidn of the cross-sectional area of the recording light beam, an illustration of shaped orifices suitable for the purpose being shown in Figure 4 of the drawing in which A presents an elliptical orifice, B and D triangular, and C a diamond-shaped opening. The beam of light passing through the orifices A, C and D will produce a path of exposure in which the central zone is more intensely illuminated than the marginal portions, as will be clear. With the orifice shown at B, a record tracing is secured which gradually changes the intensity of exposure from one side to the other of the record path to produce a final groove having one side perpendicular to the surface of the plate to compensate for the lateral pressure of the groove against the In order to produce the overrunning of the spot of light along the path of the beam in the manner already referred to, the elongated orifices shown in Figure 4 are arranged with their lengths lying in the direction of travel of the plate 2, as is indicated in Figure 5, while the movement of the shutter 9 and the orifice is transverse the longer axis of the orifice, as is also indicated in this figure.

While the structural arrangement of redegree.

is a preferred one, I may, in an alternative construction, mount the light, source upon an operating lever 15 between the diaphragm center and the orifice 12 so that the orifice, instead of traversing the path of the beam, moves bodily with it. In this case the source of light is preferably mounted at the pivotal point of the operating bar or lever 15in order that it may interfere as little as possible with the action of the diaphragm. In either construction, whether the orifice is carried by the lamp casing or contained in a separate shutter, the size of the orifice and the distance by which it is spaced from the surface of the plate 2 is extremely small so that a sharply defined path of exposure sufficiently fine. and narrow for the purpose, is obtained. In actual practice I have found that an orifice .005 of an inch in width and placed one-thirty-second of an inch from the plate has given satisfactory results.

The record which I produce by means of the apparatus described is preferably formed on plates or films of fine grain in order to insure in a still greater degree the sharpness of the lateral margins, and I develop the negative records thus formed in such a way as to secure a high degree of contrast. I preferably preserve the negative record as a master and use it in the production of positive records in black and white from which relief records are produced, although the negative record may be used directly in the production of records in relief. By my preferred method I copy the negative in black and white by photographic means upon aplate or film and obtain a positive in which the original cording lamp and shutter already described light tracing representing the vibrations of a the diaphragm is represented in the form of a clear or-white sinuous line which is intensely clear at the center but gradually becomes dark or opaque toward the lateral margins. I may increase the darkening effect toward the margins to any desired extent and without affecting the sharpness of the margins which was definitely established in the negative, by exposing in diffused light so that light falls behind the dark tracing on the negative to the desired In order to obtain a relief record'from the positive record in black and white obtained by the printing process last referred to, I attach to the film side of the positive plate -a gelatine plate having a thickness equal at least to the depth of the finished relief I desire to obtain. I then place the positive with the attached gelatine plate in the gelatine has occurred, I squeegee the,

gelatine to the positive, sensitize with am-- sensitized gelatine attached thereto tolight- I; passing through the positive plate fromthe backthereof in order that the diachromated;

material which is rendered non-soluble by the..]ight may lie against and adjacent the plate supported side of the gelatine so as to insure the firm attachment of the insoluble matter to the plate.

After exposure, I develop the gelatine plate in hot Water in a manner well-known in the art and thus secure a relief record which is the reverse of the final record in that the tracing is in raised or cameo form. An impression of this relief record may be made in soft lead or other material in a hydraulic press or by a molding process. From this impression as a basis the operation of producing records suitable for use in sound-reproducing machines may take place in the usual manner.

What I claim is:

' 1. The method of making a sound record,

which consists in photographically recording on a relatively movable sensitized surface the movements of a sound-actuated member by means of a beam of parallel light rays projected from a relatively small elongated source of light placed parallel to and'with its length lying in the direction of movement of the relatively movable sensitive surface.

2. The method of making a sound record, which consists in photographically recording on a relatively moving sensitized surface the movements of a sound-actuated member by means of light projected from a source through an adjacent transversely me ses.

ments of a sound-actuated memberby means of light projected fromuan adjacent source and through an orificelplacedfin such close relation to the surface that substantially no diffraction occu,rs ,,inemploying the negat ve thus produced :toff form. a positive "record in which the. movements of. the soundactuated mcmber arejrecorded in the. form of a transparent 1ine in. applying gelatine to the positive,recordfthus .formed, in sensltizing the. gelatine with dich romatejdn exposlng the dichromate sensitized gelatine to lightpassmg through the ipositive record, and in treating the. dichromat rsen si'tized gelatine to produce a reco rdl' in which the movements, of the .soi 1i1daotua t ec li member are' mamfestedin the form 'of an elevated.

ridge.

t. The method of making a sound record, 7

which consists in photographically. recordmg on a sensitized-surface ,the movements of a sound-actuated ..member by" means of a transversely elongated beam of parallel light rays controlled b.y,..tli1e'. movements or said sound-actuated"member, the cross-sec tional area ofsaid bea m having a conformation such as to increase the intensity of light at the central portion .of the path of exposure.

'HARTWELL W. -WEBB... 

